JP6703759B2 - Method for producing TiAl intermetallic compound powder and TiAl intermetallic compound powder - Google Patents

Description

The present invention relates to a TiAl intermetallic compound powder manufacturing method and a TiAl intermetallic compound powder.

TiAl intermetallic compounds containing TiAl, Ti ₃ Al, and TiAl ₃ have low density and excellent high-temperature strength, so they are useful lightweight heat-resistant materials as structural parts for various equipment in the aerospace and power generation fields. Is being applied to.
By the way, the TiAl intermetallic compound is a material having poor ductility and difficult to machine. Therefore, when a TiAl intermetallic compound having a predetermined shape is prepared, a powder of TiAl intermetallic compound is prepared and subjected to various powder metallurgy methods (for example, sintering, hot isostatic pressing, metal powder injection). A method of forming a near net shape by a molding method or an additive manufacturing method (also referred to as 3D printing or additive manufacturing technology) is practical. Then, a method of cutting the surface of the TiAl intermetallic compound formed in the near net shape to finish the final shape of various parts is practical.

As a method of obtaining the TiAl intermetallic compound powder, a method of "melting an alloy containing a TiAl intermetallic compound as a main component and rapidly solidifying the droplets obtained by the melting to obtain a metal powder" has been proposed. (Patent Document 1).

JP, 2008-208432, A

The method of Patent Document 1 is an effective method for refining the structure of the TiAl intermetallic compound powder. It is said that if the TiAl intermetallic compound powder having a fine structure is used, for example, when the powder is formed by sintering, the above-mentioned fine structure can be maintained, so that strength can be imparted to the molded product.
However, even a molded product obtained by such a method has room for improvement in its strength. In other words, if there are many pores (voids) inside the TiAl intermetallic compound powder, some voids due to the above-mentioned pores also remain inside the molded product, and the mechanical properties and reliability of the molded product are improved. Can be lowered.

An object of the present invention is to provide a method for producing a TiAl intermetallic compound powder capable of reducing pores inside the TiAl intermetallic compound powder, and the TiAl intermetallic compound powder.

The present invention is a method for producing a TiAl intermetallic compound powder in which a cutting piece of a TiAl intermetallic compound is passed through a thermal plasma flame to be spheroidized. And, preferably, it is a method for producing a TiAl intermetallic compound powder satisfying one or more of the following requirements.
-The size of the above cutting pieces is 500 μm or less.
The power of the above thermal plasma flame is 10 to 250 kW.
-The above-mentioned thermal plasma flame is a high frequency plasma flame.
The working gas of the above thermal plasma flame is an inert gas.
The carrier gas used to supply the cuttings in the area of the thermal plasma flame is an inert gas.

Further, the present invention is a TiAl intermetallic compound powder having a cross-section porosity of 0 to 0.4 area %. And, it is preferably a TiAl intermetallic compound powder satisfying one or more of the following requirements.
-Area circularity in the secondary projection image is 0.9 or more in 90% or more of the whole.
The particle diameter is 1 to 250 μm in 50% particle diameter (D50) of the volume-based cumulative particle size distribution.
-Ingredient composition is% by mass, Al: 10 to 80%, balance Ti and impurities. Further, it further contains one or two elemental species of Nb: 20.0% or less and Cr: 20.0% or less, or V, Ta, Mn, B, Si, C, W, 20.0% or less of each of one or more elemental species of Y is contained.
-Used in powder metallurgy or additive manufacturing.

According to the present invention, it is possible to reduce pores inside the TiAl intermetallic compound powder.

It is a drawing substitute photograph which shows an example of the cross section of the TiAl intermetallic compound powder of the example of this invention. It is a drawing substitute photograph which shows an example of the cross section of the TiAl intermetallic compound powder of a comparative example. 1 is a structural diagram showing an example of a thermal plasma processing apparatus for performing a spheroidizing process according to the present invention. 5 is a drawing-substituting photograph showing an example of the external shape of the cutting piece used in Example 2 and the TiAl intermetallic compound powder produced from this cutting piece. FIG. 5 is an elemental mapping diagram in which the cutting piece used in Example 2 and the Al concentration in the cross section of the TiAl intermetallic compound powder produced from this cutting piece are analyzed by EPMA (electron beam microanalyzer). 5 is a photograph as a substitute for a drawing showing an example of the external shape of the cutting piece used in Example 3 and the TiAl intermetallic compound powder produced from this cutting piece. FIG. 5 is an element mapping diagram in which the cutting piece used in Example 3 and the Al concentration in the cross section of the TiAl intermetallic compound powder produced from this cutting piece are analyzed by EPMA.

Each constituent element of the present invention will be described below.

(1) In the method for producing a TiAl intermetallic compound powder of the present invention, a cutting piece of the TiAl intermetallic compound is passed through a thermal plasma flame to be spheroidized.
Conventionally, TiAl intermetallic compound powder has been manufactured by a method of "melting an alloy containing a TiAl intermetallic compound as a main component and rapidly cooling and solidifying the droplets obtained by the melting to obtain a metal powder". And about this conventional method, the method proposed concretely was the "plasma rotating electrode method" and the "gas atomizing method" (patent document 1).
According to the plasma rotating electrode method, first, a base material (ingot) of a TiAl intermetallic compound is prepared as a starting material. Then, by directly irradiating the tip of the rotating electrode with plasma using the base material as a rotating electrode, droplets having the component composition of the TiAl intermetallic compound melted at the tip of the base material are scattered. .. Then, the scattered droplets are solidified and TiAl intermetallic compound powder is obtained.
Further, according to the gas atomizing method, a molten metal having a component composition of TiAl intermetallic compound is prepared as a starting material. By applying a high-pressure jet of gas to the fine stream of this molten metal, the scattered droplets are solidified, and TiAl intermetallic compound powder is obtained.

In the case of the plasma rotating electrode method, it is necessary to prepare an ingot as a cylindrical electrode in advance, which results in an increase in cost due to an increase in manufacturing steps. Further, in the case of the plasma rotary electrode method, it is not easy to produce a fine powder having a particle size of 100 μm or less.
Further, in the case of the gas atomizing method, while blowing an inert gas (cooling gas) such as argon, the molten metal is made into droplets and solidified, so that the gas is entrained inside and many pores are easily formed inside the powder after solidification. ..

On the other hand, in the case of the present invention, first, the above-mentioned starting material is a “cutting piece” of a TiAl intermetallic compound. In other words, if it is a cutting piece, it is easy to adjust the size (volume) corresponding to the target TiAl intermetallic compound powder from the beginning, so as in the gas atomizing method, it is possible to “spray a high-pressure gas” in a molten state and set it to a predetermined value. It is not necessary to divide the powder into the size of the powder, and it is possible to remove the factor of forming pores inside the TiAl intermetallic compound powder. Further, by using the cutting pieces, it is easy to adjust the particle size of the TiAl intermetallic compound powder. The size of the cut pieces can be adjusted by appropriately performing pulverization, classification and the like. In this case, it is preferable to adjust the size (length) of, for example, 500 μm or less by counting the processing capacity in the spheroidizing process described later. It is preferably 400 μm or less, more preferably 300 μm or less, and further preferably 200 μm or less. Further, it is preferably 30 μm or more, more preferably 40 μm or more, still more preferably 50 μm or more.

Since the TiAl intermetallic compound is a material having poor ductility, the cutting pieces produced when cutting this material are likely to have a granular shape without being connected for a long time. Therefore, also from this fact, the above-mentioned particle size adjustment is easy.
In addition, in the case of the above-mentioned cutting pieces, in order to directly grind a large material, the hydrogen content of the initial (starting material), such as "ground pieces" obtained by combining hydrogen embrittlement and grinding of the material Since it does not increase, it is also advantageous for reducing the hydrogen content in the TiAl intermetallic compound powder. And by this, the TiAl intermetallic compound powder having a hydrogen content of less than 0.1 mass% can be easily obtained.

Regarding the size of the above cutting pieces, if the utilization of a thermal plasma flame in the spheroidizing treatment described later is counted, the larger cutting pieces have an excess of Al, which is the main component of the TiAl intermetallic compound. It is advantageous in that the volatilization amount can be reduced. This is considered to be because when the cutting pieces are passed through a thermal plasma flame, the Al component having a low melting point is easily evaporated, and the small cutting pieces are easily affected by this. Therefore, the size (length) of the cutting pieces is preferably 70 μm or more, more preferably 80 μm or more, and further preferably 90 μm or more to prevent excessive volatilization of Al from the cutting pieces during the spheroidizing treatment. can do. This makes it possible to suppress component fluctuations from the starting material. Further, it is possible to suppress the difference in Al concentration that may occur between the produced TiAl intermetallic compound powders.

Then, in the case of the present invention, the TiAl intermetallic compound powder can be obtained by subjecting the above-mentioned cutting pieces to the “spheroidizing treatment” in which the cutting pieces are passed through a thermal plasma flame. The spheroidizing treatment is to pass the starting material such as smashed metal through a high-temperature thermal plasma flame, and the spheroids passing through the area of the thermal plasma flame are melted and spheroidized by the surface tension. The atomized small pieces (droplets) are solidified and collected after leaving the area of the thermal plasma flame, so that the powder has high sphericity (for example, the area circularity obtained by image analysis of the secondary projection image is 0. This is a method capable of producing powders of .9 or more). And in the obtained TiAl intermetallic compound powder, the area circularity in the secondary projection image is 0.9 or more in 90% or more of the whole. It is preferably 0.95 or more. Regarding the above "number of 90% or more of the whole", the area circularity of approximately 10,000 TiAl intermetallic compound powders can be measured. When the number of measured TiAl intermetallic compound powders is 10,000 or more, the numerical value of the content ratio of the area circularity as a whole becomes stable. Such a spheroidizing treatment can be performed, for example, by the thermal plasma processing apparatus of FIG. 3 (the structure of the thermal plasma processing apparatus of FIG. 3 will be described in the embodiment).
The area circularity in the secondary projection image can be measured for the TiAl intermetallic compound powder having a circle equivalent diameter of 1 μm or more in the secondary projection image.

With the above-mentioned spheroidizing treatment, when the TiAl intermetallic compound is in a droplet state in which gas is easily taken in (that is, when passing through a thermal plasma flame), the amount of gas existing around it is small. Therefore, there is little opportunity for the droplets to come into contact with a large amount of gas, and it is possible to reduce the factor of forming pores inside the TiAl intermetallic compound powder. And, in the state of droplets, the small amount of gas existing around the droplets means that the amount of reactants that can react with the droplets is also small. Therefore, since the cleanliness of the powder after solidification can be maintained high by this, the above spheroidizing treatment is a suitable method only for treating the TiAl intermetallic compound which is an active metal. And by the above, for example, a fine TiAl intermetallic compound powder having a particle diameter of 100 μm or less can be manufactured at low cost.

At this time, the electric power of the thermal plasma flame during operation is preferably 10 kW or more. By increasing the electric power of the thermal plasma flame, it becomes easier to promote spheroidization. It is preferably 12 kW or more.
On the other hand, there is no particular limitation on the upper limit of the electric power of the thermal plasma flame during operation. However, for example, it can be set to 250 kW or less. Further, it can be set to 200 kW or less, 150 kW or less, and 100 kW or less. Further, it can be set to 50 kW or less, 40 kW or less, and 30 kW or less. Then, by reducing the power of the thermal plasma flame, it is possible to reduce the excessive volatilization amount of Al, which is the main component of the TiAl intermetallic compound. It is preferably 20 kW or less, more preferably 17 kW or less, and further preferably 14 kW or less. This makes it possible to suppress component fluctuations from the starting material. Further, it is possible to suppress the difference in Al concentration that may occur between the produced TiAl intermetallic compound powders.

Further, it is preferable that the thermal plasma flame is a “radio frequency (RF) plasma flame”. By using the thermal plasma flame as the RF plasma flame, it is possible to form a high temperature portion of about 5000 to 10000K. As a result, the cutting pieces passing through the thermal plasma flame are exposed to a high temperature, the surface and the inside thereof are instantly melted and spherical due to the surface tension, so that the solid particles of the TiAl intermetallic compound powder after solidification It is suitable for improving the degree and further reducing internal pores.
As the "working gas" for generating the thermal plasma, it is preferable to use an inert gas such as argon having low reactivity. The inert gas is not a mixed gas but an inert gas except impurities. It is also possible to use hydrogen as the working gas. However, in this case, the hydrogen content in the TiAl intermetallic compound powder after solidification may increase. Then, in order to obtain a TiAl intermetallic compound powder having a regulated hydrogen content, dehydrogenation treatment such as heating the solidified TiAl intermetallic compound powder in a reduced pressure atmosphere or in a vacuum is required. Therefore, it is preferable that the working gas is an inert gas. By this, the hydrogen content of the TiAl intermetallic compound powder can be reduced to, for example, 0.002 mass% or less, or 0.001 mass% or less.
These working gases can also be utilized as a carrier gas used to supply the cutting debris to the area of the thermal plasma flame.

(2) The TiAl intermetallic compound powder of the present invention has a porosity of 0 to 0.4 area% in its cross section.
When the powder of TiAl intermetallic compound is used and it is molded by various powder metallurgy or additive manufacturing methods, the pores inside the powder can be reduced if the pores inside the powder are reduced beforehand. It is effective in improving the strength of the product. Specifically, it is a TiAl intermetallic compound powder in which the ratio of the area of the pore portion to the cross-sectional area of the powder (that is, the porosity in the cross section of the powder) is "0 to 0.4 area %". It is preferably 0.3 area% or less. It is more preferably 0.2 area% or less. More preferably, it is 0.1 area% or less. Then, these porosities can be achieved by the method for producing the TiAl intermetallic compound powder of the present invention described above.

The cross section of the TiAl intermetallic compound powder for measuring the porosity is ideally a cross section divided at the center position of the powder (that is, a cross section whose diameter is the particle diameter). However, it is not practical to accurately expose such a cross section with individual powders. In the present invention, according to the general procedure for preparing a sample for microscopic observation, first, a set of TiAl intermetallic compound powders is arranged so that a plurality of the powders are arranged in a random state so that a certain thickness can be secured. Embed in. Next, one surface of the resin in which the plurality of powders are embedded is polished. Then, the porosity in the cross section of the plurality of powders exposed on the polished surface may be measured.

FIG. 1 and FIG. 2 are optical micrographs (magnification: 100 times) showing an example of a cross section of the TiAl intermetallic compound powder of the present invention example and the comparative example, respectively. In these micrographs, a white circular shape is a cross section of the TiAl intermetallic compound powder. And what is confirmed in black inside the white circular shape is a pore. On the other hand, in the above-mentioned white circular shape, the black circular shape is a trace of the TiAl intermetallic compound powder falling off from the resin during polishing. The porosity of the cross section of the TiAl intermetallic compound powder can be obtained by subjecting this micrograph to image processing or the like. The porosity to be obtained is obtained by measuring the porosity of about 500 TiAl intermetallic compound powders, including the TiAl intermetallic compound powders whose pores are not confirmed in the cross section, and taking the porosity (average porosity) as a whole. be able to. When the number of TiAl intermetallic compound powders whose porosity is measured is 500 or more, the numerical value of the porosity as a whole becomes stable.

The component composition of the TiAl intermetallic compound according to the present invention can be, for example, a basic component composition of Al: 10 to 80% by mass and balance Ti (including impurities). Further, in this component composition, one or two elements of Nb: 20.0% or less and Cr: 20.0% or less are further added to the extent that the powder maintains the form of TiAl intermetallic compound. Seeds can be included. And, the total of these elemental species is preferably 20.0% or less.
Nb is preferably 0.1% or more, more preferably 1.0% or more, still more preferably 2.0% or more, still more preferably 3.0% or more, and particularly preferably 4.0% or more. Further, Nb is preferably 16.0% or less, more preferably 13.0% or less, still more preferably 10.0% or less, still more preferably 6.0% or less.
Regarding Cr, it is preferably 0.1% or more, more preferably 0.5% or more, further preferably 1.0% or more, still more preferably 1.5% or more, and particularly preferably 2.0% or more. is there. Further, Cr is preferably 16.0% or less, more preferably 13.0% or less, further preferably 10.0% or less, still more preferably 6.0% or less, and particularly preferably 3.0% or less. is there.

In addition to the above Nb and Cr, one or more elemental species of V, Ta, Mn, B, Si, C, W and Y may be contained as impurities, or powder. Can be contained in an amount of 20.0% or less, respectively, within a range in which the form of TiAl intermetallic compound is maintained. Preferably, each can be 0.1% or more. Further, preferably, the total of these element species is 20.0% or less, or 0.1% or more.
The above component composition can be obtained by collecting 0.1 g or more of TiAl intermetallic compound powder and measuring it.

The TiAl intermetallic compound powder of the present invention can have a particle size of, for example, 1 to 250 μm in 50% particle size (D50) of the cumulative particle size distribution based on volume. Further, the particle diameter according to D50 can be 150 μm or less. Further, a fine TiAl intermetallic compound powder having a particle diameter by D50 of 100 μm or less, or even 50 μm or less can be used. The lower limit of the particle diameter based on D50 can be set to 5 μm in order to secure the fluidity of the TiAl intermetallic compound powder. The lower limit can be set to 10 μm. The TiAl intermetallic compound powder of the present invention is suitable as a raw material powder used for producing a molded product by various powder metallurgy methods and additive manufacturing methods.

FIG. 3 is a structural diagram showing an example of the RF thermal plasma processing apparatus. This RF thermal plasma processing apparatus has a cylindrical plasma generation space with a diameter of 50 mm. The thermal plasma generation unit is composed of an inductively coupled RF plasma torch. This configuration has a plasma generation space 2 partitioned by a cooling wall 1, a high frequency coil 3 provided outside the plasma generation space 2, and a working gas supply unit 4 for supplying a working gas from one side in the axial direction of the high frequency coil 3. Have. The RF thermal plasma flame is generated by supplying a working gas from the supply unit 4 and applying a voltage to the high frequency coil 3.
Further, this thermal plasma processing apparatus includes a powder supply nozzle 6 for supplying a carrier gas and small particles as a starting material into a thermal plasma flame 5 generated inside the high-frequency coil 3, and a downstream side of the thermal plasma flame 5. And a gas exhaust unit 8 for exhausting gas from the chamber 7.

Using this RF thermal plasma processing apparatus, the cutting pieces of TiAl intermetallic compound were subjected to spheroidizing treatment to produce TiAl intermetallic compound powder (particle diameter: about 45 to 150 μm). The D50 of each powder was measured for about 3 g of TiAl intermetallic compound powder using a laser diffraction/scattering particle distribution measuring device “MT3300” manufactured by Microtrac Bell. Further, the area circularity in the secondary projection image was 0.95 or more in 90% or more of the manufactured TiAl intermetallic compound powders. At this time, the area circularity in the secondary projection image was measured for 20,000 TiAl intermetallic compound powders using a particle image analyzer “Morhologi G3” manufactured by Malvern Instruments.
The cut pieces were prepared by cutting the ingot having the composition shown in Table 2 as a starting material. The cutting pieces were needle-shaped, and their length was adjusted to around 45 to 200 μm by crushing and classifying. The plasma operating conditions during the spheroidizing treatment are shown in Table 1. The pressure inside the chamber 7 was set to a negative pressure of −0.02 MPa with respect to the atmospheric pressure.

On the other hand, the above-mentioned ingot was melted, and a gas atomizing method using Ti as an injection gas and a cooling gas was carried out on this molten metal to prepare a gas atomized powder of a TiAl intermetallic compound. Then, this gas atomized powder was classified so as to have a particle diameter of about 45 to 150 μm to obtain a TiAl intermetallic compound powder (the particle diameter by D50 is shown in Table 2). Among the TiAl intermetallic compound powders after classification, the number of powders having an area circularity of less than 0.95 in the secondary projection image exceeded 20% of the whole. At this time, the area circularity in the secondary projection image was measured for 20000 pieces of TiAl intermetallic compound powder using the same apparatus as described above.

Then, with respect to each of the TiAl intermetallic compound powders produced by the above spheroidizing treatment and gas atomizing method, the porosity observed in the cross section was measured according to the above-described procedure. Moreover, the component composition was also analyzed. The analysis of the component composition was performed by collecting 0.1 g or more of TiAl intermetallic compound powder according to the analysis method of each elemental species. Regarding metal elements, the contents of Al, Nb, and Cr were analyzed by ICP emission spectroscopy with respect to 0.25 g of TiAl intermetallic compound powder. Regarding the gas element, with respect to 0.3 g of TiAl intermetallic compound powder, the oxygen content was analyzed by an inert gas dissolution-infrared absorption method, and the hydrogen content was analyzed by an inert gas dissolution-thermal conductivity method (cutting). The same is true for one piece). The results are shown in Table 2 together with the component composition of the starting material (or cutting piece) and the particle size of D50.

From the results of Table 2, the porosity of the TiAl intermetallic compound powder 4 produced by the gas atomization method was 2.2 area %. On the other hand, the porosities of the powders 1 to 3 of the TiAl intermetallic compound of the present invention produced by the spheroidizing treatment were suppressed to 0.4 area% or less.
When the component compositions of the powders 1 to 3 of the present invention are evaluated, the component composition (Al content) of the powders 2 and 3 having a low maximum output during the spheroidizing treatment is different from the component composition of the starting material. Was small. In addition, the powder 3 in which hydrogen was not used as the working gas during the spheroidizing treatment had a low hydrogen content.

The TiAl intermetallic compound cutting pieces were subjected to spheroidizing treatment under the operating conditions 11 and 12 in Table 3 by using the RF thermal plasma processing apparatus of FIG. 3 to produce TiAl intermetallic compound powder. The cut pieces were needle-shaped and their lengths were adjusted as shown in Table 3. The appearance of this cut piece is shown in the scanning electron micrograph (magnification 100 times) of FIG. The plasma operating conditions during the spheroidizing treatment were that the operating gas was Ar gas: 86 L/min (nor) and the carrier gas was Ar gas: 4 L/min (nor). The pressure in the chamber was a negative pressure of −0.02 MPa with respect to the atmospheric pressure.
On the other hand, a gas atomized powder of TiAl intermetallic compound different from that of Example 1 was also prepared. The gas atomized powder is classified so that the particle size is about 45 to 150 μm.

The particle diameter by D50 and the area circularity in the secondary projection image of the TiAl intermetallic compound powder produced by the above spheroidizing treatment and gas atomizing method were measured. For the measurement, the particle diameter according to D50 was measured in the same manner as in Example 1, and the area circularity was measured for 10000 TiAl intermetallic compound powders. Regarding the area circularity, as a result of the measurement, the TiAl intermetallic compound powder produced by the spheroidizing treatment has an area circularity of 90% or more of all the individual powders under any operating condition. It was 0.95 or more. The external shape of each TiAl intermetallic compound powder is shown in the scanning electron micrograph (magnification 100 times) of FIG.
In the TiAl intermetallic compound powder produced by the gas atomization method, the number of powders having an area circularity of less than 0.95 exceeded 20% of the total of the individual powders.

For each of the above TiAl intermetallic compound powders, the porosity observed in the cross section was measured according to the procedure described above. Moreover, the component composition was also analyzed. The analysis of the component composition followed the same procedure as in Example 1 (the same applies to the cut pieces). The results are shown in Table 4 together with the composition of the cut pieces and the particle size of D50.

From the results in Table 4, the porosity of the TiAl intermetallic compound powder of the present invention produced by the spheroidizing treatment was suppressed to 0.4 area% or less. Then, when the component compositions of the powders 11 and 12 of the present invention were evaluated, the Al content of the powder 12 in which the cut pieces to be processed was large had little variation from the component composition of the cut pieces.

Also, regarding the difference in Al concentration that may occur between the individual manufactured TiAl intermetallic compound powders, the difference in concentration of the powder 12 in which the cut pieces to be processed was large was suppressed. FIG. 5 is an elemental mapping diagram (magnification: 100 times) when the Al concentration in the cross section of the TiAl intermetallic compound powders 11 and 12, including that of the cut pieces, is analyzed by EPMA. For this analysis, an electron beam microanalyzer "JXA-8900R" manufactured by JEOL Ltd. was used. In addition, in the result of the cutting pieces, the cutting pieces displayed smaller than the actual size have the length direction facing the analysis surface (paper surface side).
In this element mapping diagram displayed in black and white (actually, it is displayed in color according to the concentration index of the Al component "by color coding" shown in the figure), the color tone is almost the same as that of the cutting piece. Is a powder having a low Al concentration (that is, a powder in which an Al component is volatilized during the spheroidizing treatment). It can be seen that such powders having a low Al concentration are often found in those having a small particle size.

Using the RF thermal plasma processing apparatus of FIG. 3, TiAl intermetallic compound cutting pieces were spheroidized under the operating conditions 21 and 22 in Table 5 to produce TiAl intermetallic compound powder. The cut pieces were needle-shaped and their lengths were adjusted as shown in Table 5. The appearance of this cut piece is shown in the scanning electron micrograph (magnification 100 times) of FIG. The plasma operating conditions during the spheroidizing treatment were that the operating gas was Ar gas: 86 L/min (nor) and the carrier gas was Ar gas: 4 L/min (nor). The pressure in the chamber was a negative pressure of −0.02 MPa with respect to the atmospheric pressure.

The particle diameter by D50 and the area circularity in the secondary projection image of the TiAl intermetallic compound powder produced by the above spheroidizing treatment were measured. For the measurement, the particle diameter according to D50 was measured in the same manner as in Example 1, and the area circularity was measured for 10000 TiAl intermetallic compound powders. Regarding the area circularity, as a result of the measurement, the TiAl intermetallic compound powder produced by the spheroidizing treatment has an area circularity of 90% or more of all the individual powders under any operating condition. It was 0.95 or more. The external shape of each TiAl intermetallic compound powder is shown in the scanning electron micrograph (magnification 100 times) of FIG. It can be seen from FIG. 6 that the powder having a high maximum output during the spheroidizing treatment has a high sphericity.

For each of the above TiAl intermetallic compound powders, the porosity observed in the cross section was measured according to the procedure described above. Moreover, the component composition was also analyzed. The analysis of the component composition followed the same procedure as in Example 1 (the same applies to the cut pieces). The results are shown in Table 6 together with the composition of the cut pieces and the particle size of D50.

From the results of Table 6, the porosity of the TiAl intermetallic compound powder of the present invention produced by the spheroidizing treatment was suppressed to 0.4 area% or less. Then, when the component compositions of the powders 21 and 22 of the present invention example are evaluated, the Al content of the powder 22 whose maximum output during the spheroidizing treatment was low has little variation from the component composition of the cutting pieces, and Volatilization of Al was also suppressed.

Also, regarding the difference in Al concentration that may occur between the produced TiAl intermetallic compound powders, the difference in concentration of the powder 22 that had a low maximum output during the spheroidizing treatment was suppressed. FIG. 7 is an elemental mapping diagram (magnification 100 times) when the Al concentration in the cross section of the TiAl intermetallic compound powders 21 and 22 is analyzed by the same EPMA as in FIG. 5 together with that of the cut pieces.

1 Cooling Wall 2 Plasma Generation Space 3 High Frequency Coil 4 Working Gas Supply Section 5 Thermal Plasma Flame 6 Powder Supply Nozzle 7 Chamber 8 Exhaust Device

Claims (12)

A cutting piece of TiAl intermetallic compound obtained without hydrogen embrittlement is passed through a thermal plasma flame to be spheroidized, and the working gas of the thermal plasma flame is an inert gas, and TiAl after the spheroidizing treatment is performed. A method for producing a TiAl intermetallic compound powder, characterized in that the intermetallic compound powder is not subjected to dehydrogenation treatment . The method for producing a TiAl intermetallic compound powder according to claim 1, wherein the size of the cut pieces is 500 μm or less. The method for producing a TiAl intermetallic compound powder according to claim 1 or 2, wherein the power of the thermal plasma flame is 10 to 250 kW. The method for producing TiAl intermetallic compound powder according to claim 1, wherein the thermal plasma flame is a high-frequency plasma flame. The method for producing a TiAl intermetallic compound powder according to any one of claims 1 to 4 , wherein the carrier gas used to supply the cutting pieces to the region of the thermal plasma flame is an inert gas. A TiAl intermetallic compound powder having a porosity in a cross section of 0 to 0.4 area% and a hydrogen content of 0.002 mass% or less . The TiAl intermetallic compound powder according to claim 6 , wherein the area circularity in the secondary projection image is 0.9 or more in 90% or more of the whole. The TiAl intermetallic compound powder according to claim 6 or 7 , wherein the particle diameter is 1 to 250 µm in 50% particle diameter (D50) of volume-based cumulative particle size distribution. The TiAl intermetallic compound powder according to any one of claims 6 to 8 , characterized in that the composition is mass%, Al: 10 to 80%, the balance being Ti and impurities. 10. The composition according to claim 9 , further comprising one or two elemental species of Nb: 20.0% or less and Cr: 20.0% or less in mass %. TiAl intermetallic compound powder. The component composition is mass% and further contains 20.0% or less of one or more elemental species selected from V, Ta, Mn, B, Si, C, W and Y. The TiAl intermetallic compound powder according to claim 9 or 10 . The TiAl intermetallic compound powder according to any one of claims 6 to 11 , which is used in powder metallurgy or additive manufacturing.

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